Heteroatoms intra-actions and oxidant-pollutant competition over BC2O sites in N, S, B-tri-doped biochar for the nonradical activation of peroxymonosulfate

Abstract

Tri-doping effect on the catalytic activity of biochar remains limitedly explored. In this study, N, S, B-tri-doped biochar was fabricated via a one-pot calcination technique. The effects of calcination temperature and boric acid (BA):thiourea (heteroatom precursors) ratio on the surface properties and catalytic performance of the biochar were systemically investigated to elucidate the heteroatoms intra-actions during the doping process. Increasing the calcination temperature from 500 to 800 °C significantly increased the BC2O content, reduced atomic percent (at.%) of S by over 95 %, and had minimal effect on graphitic N content. Increasing the BA:thiourea ratio had a generally positive effect on BC2O content and promoted pyrrolic and pyridinic N formation. Furthermore, BCO2 groups vigorously competed against S over doping sites in the biochar structure. The catalytic performance of the tri-doped biochar as peroxymonosulfate (PMS) activator was studied using tetracycline (TC) as the model pollutant. A more effective catalytic activity can be obtained at higher calcination temperature and BA:thiourea ratio. The catalytic performance was found to withstand different water matrixes and conditions. The chemical scavenger studies and electrochemical analysis stipulated a major contribution of nonradical activation pathway with a competitive behavior between PMS and TC over adsorption and activation on the catalyst surface, with BC2O playing a decisive role in PMS activation. Lastly, based on the identified TC degradation intermediates, the TC degradation pathways were proposed, and the toxicity of these intermediates was evaluated. Overall, the results of this study show that tri-doping can potentially produce an effective PMS activator for practical applications.